A technique has been proposed which provides a V-type internal combustion engine with a variable valve timing mechanism on each of the banks, and adjusts the valve timing according to the difference of combustion conditions between the banks (for example, refer to Japanese Laid-Open Patent Publication No. 10-141097). Further, Japanese Laid-Open Patent Publication No. 2004-150397 discloses a technique for adjusting valve timing using an electric actuator.
Japanese Laid-Open Patent Publication No. 10-141097 discloses a valve timing control apparatus. The publication does not directly disclose valve timing control performed when the engine is being started. However, in normal conditions, regardless whether the engine is started cold or warm, the engine is started at generalized valve timing.
For example, the intake valve closing timing is set to a specific valve timing for starting the engine in a closing valve timing range for normal engine operation by using the variable valve timing apparatus having an electric actuator disclosed in Japanese Laid-Open Patent Publication No. 2004-150397. Such a specific intake valve closing timing is set in consideration of the balance between the rotational resistance of the engine and the driving force of a starter, such that the engine rotates smoothly and the start of the engine caused by starting combustion is completed at a relatively early stage.
However, in the case where the cylinders are divided into groups in two banks, and the valve timing is adjustable for each cylinder group as in Japanese Laid-Open Patent Publication No. 10-141097, the valve timing adjustment at one of the banks can be abnormal. In the case of Japanese Laid-Open Patent Publication No. 2004-150397, the electric actuator can malfunction.
In this case, since the malfunctioning intake camshaft does not receive the driving force for adjusting the valve timing generated, for example, by the electric actuator, the intake valve timing is moved to the most retarded state by the rotational resistance generated in the intake camshaft during cranking. Since the intake valve timing of the normally functioning bank can be adjusted, for example, by the electric actuator, the intake valve timing is set to the above mentioned specific valve closing timing.
However, considering the entire internal combustion engine, the intake valve closing timing of the malfunctioning bank is retarded compared to that of the normal engine starting, and considerable part of air that has been drawn into the combustion chambers is discharged to the intake ports from the intake valves. That is, sufficient amount of air cannot be used in the combustion at the beginning of the engine starting. Therefore, although one of the banks is functioning normally, the starting performance of the entire internal combustion engine deteriorates. Particularly, for starting an engine cold, a greater amount of intake air is needed than when starting the engine after warming. The starting performance thus can noticeably deteriorate when starting an engine cold.
Such deterioration of starting performance due to abnormal adjustment of valve timing in a bank can also occurs in a case where an engine is equipped with an apparatus for adjusting exhaust valve timing. That is, a variable exhaust valve timing mechanism incorporates a spring that advances valve opening timing. Therefore, if a variable exhaust valve timing mechanism is malfunctioning and the driving force of, for example, an electric actuator cannot be used when starting the engine, the exhaust valve timing is held excessively advanced by the urging force of the spring. The engine is thus started with the excessively advanced exhaust valve opening timing. Thus, during combustion at the beginning of the starting of the engine, the pressure in the combustion chambers can fail to be transmitted to the crankshaft through the pistons. Therefore, although one of the banks is functioning normally, the starting performance of the entire internal combustion engine deteriorates. The starting performance can noticeably deteriorate when starting the engine cold.
Such abnormality of valve timing adjustment also can occur in an internal combustion engine in which the intake valve timing and the exhaust valve timing of a single bank are adjustable. That is, deterioration of the starting performance due to an abnormality in one of the valve timing adjustments can degrade the starting performance of an entire internal combustion engine even if the other valve timing adjustment is being performed normally, and such deterioration is particularly noticeable when starting the engine cold.